Add varnish module

modules/services/web-servers/varnish/default.nix

@@ -0,0 +1,54 @@
+{ config, pkgs, ...}:
+let
+  cfg = config.services.varnish;
+in
+with pkgs.lib;
+{
+  options = {
+    services.varnish = {
+      enable = mkOption {
+        default = false;
+        description = "
+          Enable the Varnish Server.
+        ";
+      };
+
+      config = mkOption {
+        description = "
+          Verbatim default.vcl configuration.
+        ";
+      };
+
+      stateDir = mkOption {
+        default = "/var/spool/varnish";
+        description = "
+          Directory holding all state for Varnish to run.
+        ";
+      };
+    };
+
+  };
+
+  config = mkIf cfg.enable {
+
+    systemd.services.varnish = {
+      description = "Varnish";
+      wantedBy = [ "multi-user.target" ];
+      preStart = ''
+        mkdir -p ${cfg.stateDir}
+        chown -R varnish:varnish ${cfg.stateDir}
+      '';
+      path = [ pkgs.gcc ];
+      serviceConfig.ExecStart = "${pkgs.varnish}/sbin/varnishd -f ${pkgs.writeText "default.vcl" cfg.config} -n ${cfg.stateDir} -u varnish";
+      serviceConfig.Type = "forking";
+    };
+
+    environment.systemPackages = [ pkgs.varnish ];
+
+    users.extraUsers.varnish = {
+      group = "varnish";
+    };
+
+    users.extraGroups.varnish = {};
+  };
+}